1. Field of the Invention
The present invention relates to a memory element and a memory device capable of storing information by a change in an electric characteristic of a memory layer including an ion source layer and a high-resistance layer.
2. Description of the Related Art
In information devices such as a computer, as a random access memory, a DRAM (Dynamic Random Access Memory) whose operation is fast and having high density is widely used. However, since the manufacture process of a DRAM is complicated more than a general logic circuit LSI and signal process used for an electronic device, the manufacture cost is high. A DRAM is a volatile memory in which information disappears when power is turned off. A refresh operation, that is, an operation of reading written information (data), amplifying it, and writing the information again has to be performed frequently.
To address the drawback, as nonvolatile memories in which information does not disappear even when power is turned off, for example, a flash memory, an FeRAM (Ferroelectric Random Access Memory), an MRAM (Magnetoresistive Random Access Memory), and the like are proposed. In the case of the memories, written information is continuously retained for long time without supply of power. However, each of the memories has an advantage and a disadvantage. Specifically, a flash memory has high integration but has a disadvantage in operation speed. An FeRAM has limitation in microfabrication for high integration and also has a drawback in manufacturing process. An MRAM has a drawback in power consumption.
A memory element of a novel type which is advantageous particularly with respect to limitation in microfabrication of a memory element is proposed. The memory element has a structure that an ion conductor containing a metal is provided between two electrodes. In the memory element, the metal contained in the ion conductor is contained in one of the two electrodes. With the arrangement, when voltage is applied across the two electrodes, the metal contained in the electrode is diffused as ions into the ion conductor, and the resistance value of the ion conductor or the electric characteristic such as capacitance changes. For example, in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-536840, as a memory device using the characteristic, an ion conductor made of a solid solution of chalcogenide and metal is proposed. Concretely, the memory device is made of a material obtained by dissolving Ag, Cu, or Zn in AsS, GeS, or GeSe, and one of two electrodes contains Ag, Cu, or Zn.